This research project involves the development of an experimental and modeling approach to evaluate the impact (i.e. additional risk) that smoking and alcohol consumption has on agricultural workers who are routinely exposed to insecticides. Drug/chemical interactions share a common theme in which pharmacokinetic and pharmacodynamic responses are altered when chemical mixtures modify absorption rates, metabolism, tissue distribution, clearance and pharmacological action. It is hypothesized that the use of tobacco products and the consumption of alcoholic beverages at pharmacologically active doses (associated with normal use patterns) can influence key metabolic and dynamic processes modifying dosimetry and biological response following both acute and repeat exposures to insecticides. Among pesticides, organophosphorus insecticides like chlorpyrifos have been of particular concern since they are widely utilized, are neurotoxic, and a number of studies have documented both occupational and non-occupational exposures in adults and children. The mode of action for organophosphorus insecticides involves their capacity to inhibit acetylcholinesterase (AChE) activity resulting in the accumulation of acetylcholine within the cholinergic synapse thereby producing a wide range of neurotoxic responses. Previously, research on this project resulted in the development and validation of physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) models for insecticides (chlorpyrifos and diazinon). These models were shown to accurately simulate dosimetry and ChE inhibition in both rats and humans. This continuation project will focus on extending that research to evaluate the impact of prior exposure to tobacco/nicotine and ethanol. The rationale for this approach is based on the known high exposures associated with routine use of tobacco and ethanol and the capability of nicotine and ethanol to modify metabolism potentially impacting insecticide dosimetry. Additionally, nicotine and ethanol are known to impact cholinergic receptor (nicotinic and muscarinic) function which is also a key pharmacodynamic target for organophosphorus insecticides. The project will assess biological and metabolic changes, target tissue dosimetry, and dynamic responses to these pesticides following co-exposures with tobacco/nicotine and ethanol. The results will be integrated into a computational framework to quantitatively assess the health implications from insecticide exposures. The development of experimental in vitro data in human cells represents an important surrogate human experimental model system and the results will likewise be integrated into the modeling framework to help predict health effects in humans. It is fully anticipated that this approach will facilitate the understanding of a variety of complex chemical interactions as it relates to the occupational health implications of working with insecticides.